Yellow Flag Iris
Vectors of spread:
General: Yellow Flag Iris is an aquatic perennial with a fan-shaped base and yellow iris-shaped flowers.
Flowers: It has distinctive, iris-looking, bright yellow flowers, with three drooping, deep-yellow sepals and purple-brown markings surrounding three smaller upright petals.
Stem: Stems are in groups of 2-10, and grow 30cm to 1m tall.
Leaves: Narrow, sword-shaped, flattened leaves 2-3cm wide and up to 1m long with a prominent mid-rib. Leaves fan out from the base of plant. May remain green during mild winters.
Fruits: Seeds are closely packed in rows within capsules 4-8cm long.
Roots: Stout rhizomes 1-4cm thick.
Yellow Flag Iris is the only entirely yellow iris found in the wild of North America.
It is often confused with Cattail (Typha latifolia), which has round stems.
Other non-invasive irises include Oregon Iris (Iris tenax).
Habitat and Origin
Native to the Mediterranean region of Europe, Yellow Flag Iris was brought to North America as a valued horticultural plant.
Yellow Flag Iris is a wetland plant often sold as a garden ornamental. It thrives in wet areas and standing water, such as ditches, irrigation canals, marshes, stream banks, lake shorelines and shallow ponds.
Propagation and Vectors of Spread
Yellow Flag Iris spreads by floating seeds and by underground root systems, called rhizomes. A whole new plant stand can develop if a piece of rhizome breaks off and travels downstream.
The seedpods are buoyant and can remain afloat for up to 7 months, allowing it to spread over long distances down watercourses. Yellow Flag Iris also spreads by creeping rhizomes. Several hundred plants can be connected by rhizome under water. Small fragments of rhizome can break off, drift downstream, and take root, forming new stands.
Economic and Ecological Impacts
Yellow Flag Iris grows in dense mats which trap sediment, thereby choking natural waterways, irrigation canals, and flood control ditches important in infrastructure and agricultural areas.
Yellow Flag Iris outcompetes native vegetation such as cattails, sedges, and rushes. This limits the native species available for grazing, and reduces habitat for fish, amphibians, and nesting birds. It is toxic if ingested by humans or livestock and can cause skin irritation when touched.
What Can I Do?
Learn to identify Yellow Flag Iris: use the images presented in this profile page.
What to do if you spot it: You can report any Yellow Flag Iris sighting by clicking here.
If you are an eco-tourism professional, head over to the Yellow Flag Iris Patrol page!
In the Sea to Sky, the objective is to ERADICATE Yellow Flag Iris.
- At minimum, seed heads should be clipped, bagged, and disposed of to prevent further spread. Repeatedly cutting the plant material close to the ground will help to deplete the plants root reserves. The most effective method of eradication is digging up and pulling out the masses of rhizome using a sharp tool such as a mattock or crowbar. Ensure you go to the full depth of the plant (up to 30cm deep). Remove the root masses from the area to prevent re-growth from fragments. Monitor regularly for re-growth and remove any new plants that appear.
- Use of herbicides on this species is not recommended.
- There is no current effective means of biological control. Yellow Flag Iris sickens animals if eaten, causing inflammation of the stomach and intestine.
- Plant Yellow Flag Iris in a garden, no matter how well-contained its enclosure may seem.
- Move soil that has been contaminated with Yellow Flag Iris.
Revegetate after removal:
- Immediately re-vegetate disturbed wet areas with native plants such as Cattail (Typha latifolia) or other non-invasive marsh species to prevent the opportunistic invasion of these areas by species such as Yellow Flag Iris.
- Invasive Species Council of BC, Yellow Flag Iris Factsheet, https://bcinvasives.ca/documents/Yellow_Flag_Iris_TIPS_2017_WEB.pdf
- Okanagan and Similkameen Invasive Species Society, Yellow Flag Iris Factsheet, http://oasiss.ca/wp-content/uploads/2017/10/Yellow-Flag-Iris-Apr-2013.pdf
- US Department of Agriculture Natural Resources Conservation Service, Yellow Flag Iris Species Profile, https://plants.usda.gov/core/profile?symbol=IRPS
For more information, please head to the Whistler’s Worst Weeds page.